The natural intervertebral disc contains a jelly-like nucleus pulposus surrounded by a fibrous annulus fibrosus. Under an axial load, the nucleus pulposus compresses and radially transfers that load to the annulus fibrosus. The laminated nature of the annulus fibrosus provides it with a high tensile strength and so allows it to expand radially in response to this transferred load.
In a healthy intervertebral disc, cells within the nucleus pulposus produce an extracellular matrix (ECM) containing a high percentage of proteoglycans. These proteoglycans contain sulfated functional groups that retain water, thereby providing the nucleus pulposus with its cushioning qualities. These nucleus pulposus cells may also secrete small amounts of cytokines as well as matrix metalloproteinases (“MMPs”). These cytokines and MMPs help regulate the metabolism of the nucleus pulposus cells.
In some instances of disc degeneration disease (DDD), gradual degeneration of the intervertebral disc is caused by mechanical instabilities in other portions of the spine. In these instances, increased loads and pressures on the nucleus pulposus cause the cells to emit larger than normal amounts of the above-mentioned cytokines. In other instances of DDD, genetic factors, such as programmed cell death, or apoptosis can also cause the cells within the nucleus pulposus to emit toxic amounts of these cytokines and MMPs. In some instances, the pumping action of the disc may malfunction (due to, for example, a decrease in the proteoglycan concentration within the nucleus pulposus), thereby retarding the flow of nutrients into the disc as well as the flow of waste products out of the disc. This reduced capacity to eliminate waste may result in the accumulation of high levels of toxins.
As DDD progresses, the toxic levels of the cytokines present in the nucleus pulposus begin to degrade the extracellular matrix. In particular, the MMPs (under mediation by the cytokines) begin cleaving the water-retaining portions of the proteoglycans, thereby reducing their water-retaining capabilities. This degradation leads to a less flexible nucleus pulposus, and so changes the load pattern within the disc, thereby possibly causing delamination of the annulus fibrosus. These changes cause more mechanical instability, thereby causing the cells to emit even more cytokines, typically thereby upregulating MMPs. As this destructive cascade continues and DDD further progresses, the disc begins to bulge (“a herniated disc”), and then ultimately ruptures, causing the nucleus pulposus to contact the spinal cord and produce pain.
U.S. Published Patent Application 2004/0229878 discloses a procedure for the intradiscal administration of therapeutics, wherein an outer needle and an inner stylet are advanced to the annulus fibrosus, the stylet is withdrawn and replaced with an inner needle attached to a syringe, and the inner needle is advanced to the nucleus pulposus for injection of the therapeutic into the nucleus pulposus.
In other approaches, a single, fine gauge needle is used to penetrate the skin and musculature approaching the intervertebral disc. However, the drawbacks of this approach include the need for a relatively sturdy needle and an increase in the risk of infection to the disc (due to the fact that the needle that pierces the skin is also the needle that enters the disc).
To reduce the risk of infection and subsequent discitis that may result from percutaneous procedures, one common practice is to use a double needle approach in which a larger gauge needle is used to penetrate the skin and a second finer, gauge needle is passed through the first needle and into the intervertebral disc. However, this approach requires two separate needles and manual insertion of the second needle inside of the first.
Some needle systems developed for use outside of the disc area have dual needle designs. For example, in needle systems unrelated to intradiscal delivery of therapeutics, various needle systems and procedures are employed for aspirating body fluids, and some of these employ concentric multi-gauge needles. Various access needle systems designed to treat ailing tissue are made to allow a second device to pass through an outer access needle. Various extendable/retractable needle systems exist as safety devices to prevent user injury by needle sticks.
U.S. Pat. Nos. 5,871,470 and 6,245,044 disclose a set of interlocking concentric epidural-spinal needles for delivery of medicaments into the epidural and subarachnoid spaces. However, these systems contain two separate needles that the user must assemble. Neither system is pre-assembled.
U.S. Pat. Nos. 6,497,686 and 6,695,822 disclose a method and device for performing sterile endoluminal procedures using a needle system that includes two concentric needles. However, these systems do not allow for aspiration of the medicament into an attached syringe. Moreover, the distal portion of the device is designed to remain in place after the procedure is completed.